Zwiebach Letter to the WSJ

Over at his web-site, Lubos has posted a letter to the Wall Street Journal from Barton Zwiebach. The letter seriously misrepresents the current state of string theory in several ways:

string theory is an extraordinarily precise and rigorous framework where facts can be proven beyond doubt and computations give unequivocal answers.

All that is needed to confirm string theory is finding one solution that describes our universe. All that is needed to rule out string theory is showing that no solution describes our universe. An answer must exist.

Zwiebach gives the impression that there are rigorously well-defined, “extraordinarily precise” equations that characterize string theory, and all that is needed now is to solve the technical problem of finding the solutions to these equations and seeing if one of them agrees with what we observe. This is simply not true. Since we don’t know what non-perturbative string theory is or what its equations are, all equations used by string theorists to generate solutions are not “extraordinarily precise”, but are explicitly approximations, often very crude ones, whose reliability is unknown. If you look at the debate over the landscape, you will find that not only do most string theorists not believe that the solutions involved are “facts [that] can be proven beyond doubt”, many of them believe these are not real solutions to the full unknown theory at all.

Even if one does believe in the rigorous nature of the landscape solutions, Zwiebach’s claim that all one has to do is examine them to see if they agree with nature is again highly misleading. If there are 101000 or more of these solutions, all evidence is that identifying which of them have desired properties (e.g. the correct CC) is an inherently computationally intractable problem. Even if one could do this, the class of solutions that agree with all known values of the parameters characterizing the standard model seems likely to be so large that no new testable predictions would be possible.

Zwiebach also claims:

String theory has explained, for example, why black holes have entropy and temperature.

This is what Hawking did back in 1974 with a semi-classical calculation. Any theory of quantum gravity should reproduce this. What string theory adds to Hawking’s calculation is a long story, but if we manage to observe a black hole any time soon and it behaves as Hawking predicted, he’s the one who is going to get a Nobel prize for explaining “why black holes have entropy and temperature”, not string theorists.

I had been wondering what the response from string theorists would be to the public dissemination of arguments from Smolin and me about string theory. The response seen here from Distler et. al. and Zwiebach is not at all what I expected. Most serious string theorists I talk to take the reasonable attitude that string theory is still so poorly understood that it cannot be confronted with experiment, even in principle. Many publicly say that we still don’t know what “string theory” is. Zwiebach seems to believe that there now exist “extraordinarily precise” equations, with solutions that will give “unequivocal answers”. Whether this is true is a well-defined question. All he has to do is explain what these equations are, and let’s see if the string theory community will really stand by this definition and let string theory be judged accordingly.

Finally, perhaps the most surprising aspect of Zwiebach’s letter is the form in which he has chosen to distribute it. I and many people have been wondering what Lubos Motl’s colleagues in Cambridge think of the way he is defending their subject. Now at least one of them has made clear that he is fine with this and willing to encourage it.

Update: The usual response from Lubos Motl/Bill O’Reilly: an endless rant about how stupid people who disagree with him are, completely ignoring the scientific questions at issue.

I am no string theorist (I haven’t even completely digested the possibility of extra dimensions yet) but this is my opinion:
Zwiebach is a serious string theorist: in his book he explicitly states that string theory is not yet completely understood and that it makes no sharp prediction. In the letter itself Zwiebach doesn’t say there are precise equations defining string theory, only that it is a precise framework; again hinting that it is not completely developed.

I suppose that perhpas one can parse Zwiebach’s letter in some way that makes what he says technically true. But claiming to the public that you have an “extraordinarily precise and rigorous framework” and can do “computations that give unequivocal answers” is seriously misleading if the situation is that the framework is insufficiently developed to produce equations that could be used to reliably answer any questions about physics.

What Hawking showed was that there is a reason black holes have entropy and temperature, completely independent of the microscopic description. This explains these two facts, you don’t need to know the microscopic definition. Actually, he didn’t show “that” they have a temperature and radiate, for that we’ll have to find one and look at it…

The comments you make about QED are completely irrelevant. In QED the physical vacuum state is the perturbative one, so you can do most physics without worrying about non-perturbative effects. In string theory, the perturbative ground state is the wrong one, all the “backgrounds” people are working with are supposed to come from some putative non-perturbative effect. You can’t ignore non-perturbative effects, and this is why you can’t predict anything.

Robert – this completely misses Peter’s point. QED has definite equations that come about in a perfectly well-defined physical way, that can be evaluated with a certain amount of – apparently physically plausible – wishful mathematical thinking. Some people (Chris Oakley) apparently have taken it farther even than this. Yes, we know what QED means, in all its details, once the renormalization program is accepted as a tentative approach to actual calculation.

The point about black holes – which you also missed – is that what is being described by Hawking does not require a detailed microscopic theory, any more than evaluating the efficiency of a refrigerator requires quantum statistical mechanics. So the kudos for keeping your beer cold go to Carnot and Gibbs, not Ehrenfest and Landau.

Why does Hawking get so much more credit than Bekenstein? Perhaps I’m missing some historical perspective, but Bekenstein laid out a beautifully simple argument as to why black holes have entropy and that the entropy must be proportional to the surface area. I thought Hawking’s contribution was to reconcile the apparent contradiction that black hole radiant by invoking quantum mechanics?

if string theory has 10^500 vacua and the SM has 20 parameters, to check string theory in the way suggested by Zwiebach we simply need to predict and measure the first 25 digits of each one of them. It sounds like a joke.

Why would they not find him credible? He is a professor of physics at a leading institution and has a long publication record. He has also written a famous string theory textbook, based on an undergraduate course he developed and taught at MIT that received the top university teaching prize.

Does string theory really say anything about the kind of black holes which, perhaps, have been observed? I thought that Strominger-Vafa was about extremal black holes, whereas real black holes are very non-extremal.

Hawking did not show that a BH has an entropy. He showed that a quantized field in a BH background experiences particle production at a specific temperature related to the surface gravity of the black hole. From there, he expanded on Bekenstein’s claim of a generalized second law by suggesting that there are quantities (the surface gravity and area) that seem to play the role of a temperature and an entropy. So he showed that there is a quantity that is analogous to an entropy. He was very clear in making this distinction in his 1974 paper.

Why doesn’t this demonstrate the existence of a “real entropy”? An entropy counts the number of microstates consistent with a course grained description of a system. Unless you can count the microstates, you haven’t demonstrated the existence of an entropy. So when Peter states “Hawking showed was that there is a reason black holes have entropy and temperature, completely independent of the microscopic description”, that is wrong.

Even if you aren’t interested in quantum gravity, this should be clear. As Peter said, Hawking’s calculation used semi-classical gravity, where the matter is quantum mechanical but gravity is classical. So it should come as no surprise that a framework in which gravity is treated classically can not explain “why” a feature of the gravitational field has an entropy associated with it.

Peter points out that any theory of quantum gravity should reproduce this, and he’s correct. String theory, as a quantum theory of gravity, offers several examples of black holes where the microscopic degrees of freedom *can* be counted. The result is one-quarter of the area, as predicted by Bekenstein and Hawking. In that sense, String theory explains why these black holes have an entropy, as Zwiebach claimed in his letter.

Joe,
You’ve changed my words. What I wrote was about the credibility of his arguments, and was based on scientific arguments that I made in detail in the posting. Instead of addressing my points and discussing the scientific questions at issue, you put words in my mouth and make this about who has more impressive scientific credentials.

Lubos Motl is a string theorist with many publications and is a faculty member at Harvard. Do you think that the Wall Street Journal should publish one of his rants if he were to choose to send it to them?

The attempt to change the topic from the science at issue to who has the best credentials is one of the tactics I was expecting here. It’s not going to work.

Eh? If and when the WSJ receives Zwiebach’s letter they will check who he is and his credentials (professor at MIT etc), and will almost certainly publish it. If LM writes a letter to WSJ they will check on him too. If his letter is a rant they will justifiably toss it. But Zwiebach’s letter is not a rant.

I think this is all a matter of language, we don’t disagree on the science. Hawking showed that semiclassical arguments imply that black holes carry properties with the characteristics of entropy and temperature, and that any underlying quantum gravity theory has to have states that realize these properties. To me that counts as an “explanation”. Understanding the quantum states is of course a more complete explanation.

Thomas is also correct that string theory has yet to provide this kind of microscopic explanation for physical black holes, so in this case the only explanation is Hawking’s. If one wants to demand a true, complete fundamental explanation of the entropy and temperature here, one should also note that the string theory brane arguments, in the absence of a full non-perturbative theory, show just that the brane framework passes a consistency check, and a final explanation of all this still does not exist.

Anyway, I note that all of this defense of Zwiebach’s points is about the black hole issue, which is actually irrelevant to the question here, whether string theory is unpredictive, i.e. not even wrong. Is anyone willing to defend the claim that what is currently known about string theory gives “an extraordinarily precise and rigorous framework where facts can be proven beyond doubt and computations give unequivocal answers”? The only other string theorist I’ve ever heard go on like that is Lubos.

My comment was just that it should be the content of the letter that is the main deciding factor, not who wrote it. If the WSJ consults other experts and they say that Zwiebach is just wrong, should they publish it?

I honestly don’t know what they will do or how they will make a decision. Editors of a business publication are not in a very good position to figure out what is going on in the case of a contentious scientific argument in a notoriously difficult and obscure field. Good luck to them in dealing with it.

“First let’s see which if any of the letters the WSJ decides to publish. They may very well not find them credible or worth publishing. If they do, then maybe a rebuttal would be in order.”

So Joe did not change your words (though he did quote a single sentence from a three sentence paragraph). He just asked why they would have a reason to doubt Zwiebach’s credibility, and followed up with a list of reasons why they might consider him a reasonable source.

I don’t think he attempted “to change the topic from the science at issue to who has the best credentials”, even if that is “one of the tactics [you were] expecting here”. You suggested the WSJ might “very well” decide that the letter wasn’t credible, and Joe pointed out that that probably won’t be the case.

You may have meant other letters, or you may have meant that you feel like the WSJ editors won’t buy Zwiebach’s arguments, but there doesn’t seem to be anything unreasonable about Joe’s interpretation of, and response to, your exact words.

The WSJ is fundamentally a profit-making business. Unless the letters received are obviously polemics, or slander/libel, the WSJ has no reason not to publish them. What it would like best is a free-for-all flood of letters and watch the fur fly. It might even (gasp!) boost readership for a few days.

You’ve changed my words. What I wrote was about the credibility of his arguments, and was based on scientific arguments that I made in detail in the posting. Instead of addressing my points and discussing the scientific questions at issue, you put words in my mouth and make this about who has more impressive scientific credentials.

I did not change your words, I quoted your line. In any case, I was only responding to whether the WSJ would publish his letter. I simply pointed out that the WSJ will likely take into account Barton’s professional credentials when they make their decision whether to publish or not. Why wouldn’t they? I doubt that they are going to closely examine the finer points of Strominger-Vafa. By mentioning his credentials it was not meant as a comparison to anyone elses.

dear Peter, you have not quoted this part of Zwiebach letter: “theories of strong nuclear forces are equivalent to theories of gravity. Over the last two months, several new papers use string theory to describe the motion of quarks in the plasma created by the Relativistic Heavy Ion Collider at Brookhaven!”

Indeed strings have been tried as an approximation to QCD. Maybe somebody knows how good the string approximation is and what they are trying to compute?

LOL. You made a straightforward point that they might not find his letters credible in content, and you have to clarify it again and again and again and … with ppl continuously misconstruing it. Actually it makes perfect sense, since argument by authority is one of the strongest ones they have…

If this is the annoyance with one trivial paragraph you wrote, good luck in dealing with less idiotic critiques! I don’t envy you your position…

What’s discussed in the WSJ article and is at issue here is whether string theory is “Not Even Wrong” as a unified theory of particle physics and quantum gravity. Whether you can use it to solve QCD is a very different issue, there it certainly has promise. The calculation Zwiebach mentions is part of that story, a really different topic. If string theorists were just saying that they were working on a way to solve QCD, there would be no controversy here.

There’s finally a short but sweet review of “Not Even Wrong” tucked away on page 56 of the 1 July issue of New Scientist:

“String Weary

“Not Even Wrong … Reviewed by Amanda Gefter

“This is like two books in one. The first is a technical overview of the mathematical structure of the standard model of particle physics. The second is a highly readable look at the sociology of string theory. In the end, Woit ties the two together in one fell swoop by suggesting that physicists should search for answers in the unexplored symmetries of the standard model, rather than in strings. Woit is taking a shot at the string theory clique, but this book is more than that – it is a call to arms for physicists to pursue multiple paths in search of truth, not funding.”

Seeing that the powers that control Wikipedia aren’t happy with a lot of links to reviews of N.E.W. on the Woit article, perhaps Peter can sometime get around to actually putting a list of links to newspaper an magazine reviews on this blog somewhere (say somewhere low down on the right hand side of the main page). Or perhaps Peter can put up a page listing the contents of the book somewhere as he wrote long ago that he would?

I’ve seen N.E.W. on sale ONLY in large city bookshops, so far, in the U.K. So don’t get the idea it is widely available offline over here. Do you know how many copies they’ve printed? Since it’s hardback the usual figure in the U.K. for a well established London publisher is 5,000. That isn’t going to compete with the established string theory books.

In the small/major towns, the popular science shelves of bookshops are still creaking under a load of stringy speculation, with not a single copy of N.E.W. yet in sight. OK, so the Sunday Times marketing dept have have sold some after their review, and people can order it in from any bookshop, but don’t get complacent. Maybe you should take a look at the tacky publicity techniques string theorists use for their popular books? (Like tacky internet sites full of promotion gimmicks; when wrestling with pigs people must be prepared to get dirty, or lose.)

Hawking and Bekenstein showed that the entropy has to be proportional to area. They did not show what the microstates are. Moreover Hawking’s argument of thermal radiation leads to information paradox and this is where string theory (if correct) will contribute. One should be well informed on what string theorists working on black holes are trying to do before comparing their work with Hawkings.

Just who is it who you think doesn’t know what string theorists working on black holes are trying to do? It seems to be a pathology common in the string theory community to believe that non-string theorists don’t know well-known things about string theory, a pathology especially common among string theory graduate students. Just because you just learned something doesn’t mean that people who have been around this business for 30 years don’t know it.

Everyone seems to believe that the recent paper by Acharya and Douglas “shows” finiteness, when, if you look at it, you’ll see that they are just making conjectures. It’s amazing how much of this goes on in string theory, with conjectures magically being quoted by everyone as solid results.

And no, even with the kind of finiteness that Acharya and Douglas conjecture, the words “computationally tractable” definitely don’t apply in this case.

Just who is it who you think doesn’t know what string theorists working on black holes are trying to do? It seems to be a pathology common in the string theory community to believe that non-string theorists don’t know well-known things about string theory, a pathology especially common among string theory graduate students. Just because you just learned something doesn’t mean that people who have been around this business for 30 years don’t know it. ”

This is an unnecessary comment. Where do you get off jumping down his throat for not being properly deferential to you? You’ve stated, on this blog, that you aren’t interested in spending your time on quantum gravity. He is, so give him a break. He made a fair comment. There are explanations of Hawking’s contribution on this page that are wrong. Whether or not it was a mis-statement, or a question of language, is beside the point. Furthermore, he brought up the information paradox. That is relevant to the discussion.

For someone who was so worried about making this discussion about “who has more impressive scientific credentials”, that was a very telling comment.

“This is what Hawking did back in 1974 with a semi-classical calculation.”

Hmmm…The Hawking paper I have says “Received April 12, 1975.”

If you read the paper, you find Hawking and before him Beckenstein only make the argument that S + A/4 is a reasonable definition of Entropy – by using an analogy with classical thermodynamics and an earlier 1973 result for the FIRST law of thermodynamics for black holes — and not because a density of states calculation was done…
You will also discover that particle emission by black holes (the MAIN result of the paper) is REQUIRED to prevent violation of the Generalized Second Law (entropy does not decrease). Beckenstein made his analogy without this result…and so Beckenstein was technically wrong, and Hawking justly deserves the credit.

However, it is a HUGE improvement to get the result from a first principles density of states calculation. Hawking’s result applies to ALL (charge, uncharged, rotating, whatever) black holes…string theory has made a few calculations that agree with Hawking….the only question is do you believe they are valid calculations. If so…then Zwiebach is partly correct…The problem I have is these string theory papers are sometimes so weakly refereed and authored…I am not sure I believe these calculations.

This has nothing to do with “being properly deferential” to me, and has nothing to do with my comments about not wanting to spend more time thinking about quantum gravity. Anyone who has ever read any of the hundreds of overhyped promotional pieces about string theory knows that string theorists have calculations counting microstates of black holes and what an important contribution to physics they believe this to be.

Sorry, but I’m just sick and tired of being insulted as ignorant by completely clueless, arrogant string theorists, young and old, who think that this is an appropriate way to behave in response to scientific criticism of string theory. I’m not going to put up with it, and will jump down their throats when they do it, no matter who they are (except for Lubos, who is playing a wonderful role as public poster-boy of this particular pathology, and so deserves to be encouraged).

My source, I’m not proud to say, was Wikipedia, which says 1974. The SPIRES entry for the paper however also says 1974. Perhaps it was circulated earlier as a preprint before the final version was submitted to CMP.

Sure, I refer to string theory as “not even wrong”, but that is a criticism of a scientific theory and not a personal attack on anyone.

I’m quite used to being insulted as an ignorant crackpot by string theorists who don’t have a scientific argument. It does go with the territory and I’m sure there will be a lot more of it to come. But one wonderful aspect of this glorious new blog software is that when they choose to do it here, I can immediately give them a piece of my mind.

Sorry, but I’m just sick and tired of being insulted as ignorant by completely clueless, arrogant string theorists, young and old, who think that this is an appropriate way to behave in response to scientific criticism of string theory. I’m not going to put up with it, and will jump down their throats when they do it, no matter who they are…

Chill out! You have good scientific points, and most people reading your blog (even your opponents) recognize that. They can also see for themselves who is clueless and who is arrogant. When you “jump down somebody’s throat” it doesn’t help your cause. There is no need to be offensive. Stick to your scientific arguments, and you’ll be o.k.

Sure it does. You said “Just because you just learned something doesn’t mean that people who have been around this business for 30 years don’t know it.”, which means that he should know better than to try and tell you something about Hawking’s caclulation. And you said it on the same page where you accused Joe of trying to turn this into a discussion about who has more impressive scientific credentials.

In fairness, I would also be annoyed if I felt like a grad student were lecturing me about something I understand. But has he ever commented on your blog? Does he have a history of being uppity with you? How do you justify your claim that he thinks you are “ignorant”? For all you know he was trying to contribute to the discussion. But you’re upset about the way you perceive people as treating you, so you jumped on an easy target.

“find them credible”, with “them” clearly referring to letters, is not the same as what you wrote: “find him credible”

Peter,

My mistake was not putting in the full quote, so here it is:

-First let’s see which if any of the letters the WSJ decides to publish. They may very well not find them credible or worth publishing. If they do, then maybe a rebuttal would be in order.

The clear implication from this quote is that the WSJ might not find Zwiebach’s letter credible or worth publishing. Maybe that was not your intent, but a reasonable person could certainly take this as its meaning. I only pointed out that the WSJ would have good reason to treat Zwiebach as an expert on this issue, based on his scientific credentials.

When I was in graduate school, I remember looking at some of the stuff he was working on (with Minahan, I seem to recall). It was actually fascinating stuff, and although his interest in the subject matter was related to string theory, no knowledge of or regard for strings was required to appreciate these particular explorations of quantum theory. It was stuff that I would describe as having an “extraordinarily precise and rigorous framework,” in fact. It was just utterly divorced from real-world physics.

He was doing very good work on this stuff, but at the same time, he made claims about this material that were ludicrous! He was discussing the material at one fairly informal seminar, and at one point, he displayed some extremely interesting solutions to the theory. Then he claimed that he had shown that all the solutions had this form. Scribbling on a borrowed piece of paper at the back of the room, I had falsified this claim by the end of his talk, by finding a very special exact solution. I showed him the solution, and he acknowledged it was correct. (Barton is a very nice guy, and I respect him for that, at least.) A little more work showed where his reasoning had gone wrong. It looks like he had been trying to do something like inferring the properties of a function from working, term by term, with an assymptotic series–not a very reliable method.

But it’s exactly the kind of technique that would “allow” one to infer facts about nonperturbative string theory from what is known right now.

I might be remembering wrong, but the initial Hawking result was first published in a very criptic short letter to nature in 1974. It was criptic because it didn’t have much details for one to assess the validity of the result. This letter was before the CMP article.

One should be aware that if one performs Hawking’s calculation in Schwarszchild coordinates, one does not obtain radiation and entropy. On the other hand, this might not be kosher as it leads to all sorts of divergences as one approches the horizon. I forget who performed this calculation, but it was before Hawking in the early 70’s in a PRD article. I am not claiming Hawking to be incorrect. I am just pointing out that there are many inconviniences and inconsistencies with semiclassical gravity that are ignored and have never been fully resolved.

The only reference I have seen in the letter to ST as a theory of anything, and not just stringy versions of known physics (yarn theory? 🙂 ), is the Black hole entropy/temperature thing, though so far the “explaination” for the real ones is yet to come to your hometown theaters [It is absurd to say that ST explains BH entropy, as absurd as the claim it predicts gravity.], and the following sentence:

“All that is needed to confirm string theory is finding one solution that describes our universe. All that is needed to rule out string theory is showing that no solution describes our universe. An answer must exist.”

Such postdictive power would look better in a history book than any science literature. I would rather predict which one is ours and why. In fact, is the theory ever going to tell us which universe we live on or that comes as an external bit of information?
It is true in the other hand that to rule out ST it is enough to show that no solution describes our universe. That’s exactly what the Distler et al. paper attempts. If our universe violate “the bounds” steming from assumptions A,B,C (unitarity, analyticity and Lorentz invariance), any ST version having A,B,C as properties must be discarded. So far I havent seen any string theorist claiming Lorentz invariance isnt a fundamental ingridient of the theory [Besides Peter’s comments on vague ideas of David Gross]. If I remember correctly at the end of the string05 conference Lee Smolin pointed out that tests of Lorentz invariance would falsify ST, to what Ed Witten was reluctant to comment on. If LHC turns on, we dont have a light Higgs and the bounds are violated, we better start taking Gross’ ideas a bit more seriously, or perhaps also taking a closer look to LQG et al. 😉
I personally find such possiblity fascinating, though logically possible and physically unlikely…

You’re quite right, what I said was that the WSJ might not find Zwiebach’s letter credible. Anyone who has listened to many famous string theorists publicly saying that we still don’t know what string theory is might find his claims in the second paragraph of the letter to be not credible. The distinction you seem to be not able to get is that the credibility of an argument and the credibility of a person are two quite different things. I was only referring to the credibility of the arguments in the letter and I objected very much to your turning that into a comment on his credibility as a person.

The most credible person in the world will sometimes make an argument which is not credible. This doesn’t make them not the most credible person in the world, for that they have to keep making such arguments.

For the record, I think the WSJ should publish Zwiebach’s letter, even though I think part of it is scientifically inaccurate. The scientific issues are not ones they are capable of adjudicating, and having a response from a well-known string theorist to the article is quite appropriate. If they don’t publish it, it would be most likely because it is only one of several letters from that side they receive, and they do have space limitations.

I was thinking of taking “Malo Juevo” to task for not sticking to science, but on rereading his comment, it is a relevant story. The fact that you can’t infer properties of a function from properties of terms of its asymptotic series is precisely the problem at issue here.

Bob,

Yeah, this is definitely off-topic and not a useful discussion. I’ll admit that some days I do have a short fuse on this particular topic, and, as Eugene pointed out to me, would do better to ignore some people rather than respond to them.